The owners of storage tanks, smoke stacks, television towers, tall buildings and other storage bins and silos subject themselves to possible liability resulting from unauthorized use by children of the permanent ladders secured thereto. Where a child wanders onto the property on which a storage tank or silo is located, and is injured while climbing the ladder, the owner of the property may be liable. Therefore there is a need for some type of safety shield for preventing unauthorized use of the ladder.
Home-made devices for keeping children off such ladders have been used such as barbed wire wrapped around the lower rungs of the ladder, or a heavy object laid against the lower rungs of the ladder which children cannot move. The disadvantages to such types of makeshift shields are that it is sometimes difficult and time consuming for an authorized person to remove the shield so that he may ascend the ladder.
One known prior art reference which discloses an attempt to overcome such a problem is the U.S. Patent to Ludlow No. 3,225,863 where in FIG. 3, there is shown a hinged cover plate for fire escapes. This approach to the solution falls short of the mark, however, for several reasons. First of all, the safety shield does not extend around the side and rear of the ladder, so that a person having some ingenuity can reach around the safety shield and grab hold of the rungs of the ladder and pull himself up to a point above the top edge of the safety shield.
Secondly, the shield is attached to the ladder at or adjacent the ground, and it is an easy matter for one child to stand on the shoulders of another and gain access to the rungs of the ladder above the shield. If the shield were lengthened to such an extent as to prevent such unauthorized use, it would become very heavy, expensive, and difficult to install and use.
Finally, while a shield such as that shown by Ludlow may be easily installed during the initial construction of the fire escape, and the fire escape and shield may be so constructed as to be compatible with each other, there is needed a shield which is adapted to be installed on substantially all of the existing types of ladders in use today. Such ladders vary in width between side rails, distance between the rungs, and spacing between the ladder face and the support surface to which it is attached. Therefore, the hardware by which the ladder is installed must be extremely flexible, since hardware that is constructed to fit one type of ladder, may not fit any other type of ladder.
The owner of a storage tank or tower is not going to be interested in using a safety shield that is very difficult and expensive to install, as for example, if he has to send a welding team out to the site to make the installation.